Injuries to soft tissue, such as cartilage, skin, muscle, bone, tendon, and ligament, frequently require surgical intervention to repair the damage and facilitate healing. Such surgical repairs can include suturing or otherwise repairing the damaged tissue with known medical devices, augmenting the damaged tissue with other tissue, using an implant, a graft, or any combination of these techniques.
One common tissue injury involves damage to cartilage, which is a non-vascular, resilient, flexible connective tissue. Cartilage typically acts as a “shock-absorber” at articulating joints, but some types of cartilage provide support to tubular structures, such as for example, the larynx, air passages, and the ears. In general, cartilage tissue is comprised of cartilage cells, known as chondrocytes, located in an extracellular matrix, which contains collagen, a structural scaffold, and aggrecan, a space-filling proteoglycan. Several types of cartilage can be found in the body, including hyaline cartilage, fibrocartilage, and elastic cartilage. Hyaline cartilage can appear in the body as distinct pieces, or alternatively, this type of cartilage can be found fused to the articular ends of bones. Hyaline cartilage is generally found in the body as articular cartilage, costal cartilage, and temporary cartilage (i.e., cartilage that is ultimately converted to bone through the process of ossification). Fibrocartilage is a transitional tissue that is typically located between tendon and bone, bone and bone, and/or hyaline cartilage and hyaline cartilage. Elastic cartilage, which contains elastic fibers distributed throughout the extracellular matrix, is typically found in the epiglottis, the ears, and the nose.
One common example of hyaline cartilage injury is a focal articular cartilage defect in the knee. A strong impact to the joint can result in the partial removal of a cartilage fragment of various size and shape or sufficiently damage the extracellular matrix of the cartilage to cause degeneration of cartilage. If left untreated, damaged articular cartilage can restrict joint function, cause debilitating pain and may result in long term chronic diseases such as osteoarthritis, a disease characterized by cartilage breakdown and unfavorable changes in the underlying bone. As injuries to the articular cartilage tissue generally do not heal on their own, surgical intervention is often necessary to repair symptomatic lesions. The current modality of treatment consists of lavage, removal of partially or completely unattached tissue fragments. In addition, the surgeon will often use a variety of methods such as abrasion, drilling, or microfractures, to induce bleeding into the cartilage defect and formation of a clot. It is believed that the cells coming from the marrow will form a scar-like tissue that is fibrocartilaginous in nature and can only provide temporary relief to some symptoms. Unfortunately, the repair tissue does not have the same mechanical properties as hyaline cartilage and therefore degrades faster over time as a consequence of wear. Patients typically require a secondary procedure to alleviate symptoms.
More recently, experimental approaches involving the implantation of autologous chondrocytes have been used with increasing frequency. The chondrocytes are obtained by harvesting a piece of cartilage from a patient using a biopsy and then cells are extracted from the tissue sample and cultured to the appropriate numbers in the laboratory. The expanded chondrocytes are then provided to the surgeon in the form of a cell suspension or pre-loaded onto a synthetic or natural biodegradable, biocompatible scaffold for placement into the cartilage defect site. Sometimes, these living cells are placed in a three-dimensional natural or synthetic scaffold or matrix, and are kept under tissue specific culture conditions to create a transplantable function tissue replacement. If provided with the appropriate conditions and signals, the cells will proliferate, differentiate, and secrete various matrix molecules to create an actual living tissue that can be used as a replacement tissue to be implanted back into the defect site in the patient.
Other techniques for repairing damaged cartilage employ cells other than chondrocytes to produce the desired hyaline-like tissue. Stem or progenitor cells, such as the cells within fatty tissue, muscle, or bone marrow, have the potential to regenerate bone and/or cartilage in a patient. Stem cells can be from that patient, i.e., autogeneic, or from another patient, i.e., allogeneic. These progenitor cells in addition to other cells, such as cells from the synovium, are thought to regenerate cartilage tissue when placed in an environment favorable for inducing cartilage formation.
Other surgical techniques for the surgical treatment of damaged tissue include the use of surgical implants, scaffolds, or matrices. Various surgical implants have been used in surgical procedures to help regenerate cartilage without the use of cells. For example, implants can be created consisting of porous biodegradable, biocompatible polymeric matrices. Other examples include matrices derived from biopolymers such as hyaluronic acid, collagen, and fibrin. These implants are often used in conjunction with marrow stimulation techniques, such as microfracture, such that the marrow can provide the cells as well as other stimulants that will help to regenerate cartilage.
Before an implant can be placed into the patient, preparations must be made to both the defect site and the implant to ensure good integration of the implant with the cartilage surrounding the defect. The patient must be prepared by clearing the degenerate or damaged tissue from the defect site. Particularly in arthroscopic procedures where access to the surgical site is limited, clearing space at the defect site can be difficult and time consuming in attempts to minimize any trauma to the neighboring healthy cartilage and/or subchondral bone, i.e., the bone underlying the defect. The implant must also be prepared by sizing it from its laboratory-created size to match the cleared defect space in the patient. Because the implant cannot be appropriately sized until the space at the defect site in the patient has been formed and its size can be identified, the implant has to be prepared for implantation ad hoc during the surgical procedure. Errors in sizing the implant during the stress of surgery can prolong the surgical procedure and can result in repeated resizing of the tissue replacement to an acceptable size. In some cases attempts to size the implant can result in no appropriately sized implant if it has been cut to one or more unusable sizes. An unusable implant can necessitate creation of another implant in another expensive, time-consuming, and medically intrusive process followed by another attempt at implantation in the patient.
Accordingly, there remains a need for methods and devices for preparing a defect site in a patient and for preparing and placing an implant into the patient.